Achieving Fine Focus

Presentation by Keith Rickard23 April 2009

Cheap Focusing Techniques

For visual and imaging using:

• CCD Cameras

• D/SLR Cameras

• Compact Cameras

• Webcams

Methods:

• Imaging Software

• Focusing Masks

Imaging Software - Maxim DL

Imaging Software - Maxim DL

Imaging Software - Maxim DL

Hartman Mask

It’s very easy to make a mask, for example:

Focusing with a Hartman mask

Good focus is obtained by bringing the points together, but this can be difficult when you lose sight of them – has optimum focus been achieved?

A new kind of focusing mask:

Bahtintov Focus Mask

When the mask has been placed over the aperture of the telescope, the image of a star produces 3 diffraction lines.

To get accurate focus the user just simply needs to make sure the central diffraction line is exactly in the centre of the two diagonal lines by adjusting focus as show here.

How do you make one?

1) Visit http://astrojargon.net/MaskGen.aspx to obtain a SVG file (scalar vector graphic file) of you Bahtinov focusing mask. The mask design is optimised for focal length and aperture of your telescope or lens.

How do you make one?

1) Visit http://astrojargon.net/MaskGen.aspx to obtain a SVG file (scalar vector graphic file) of you Bahtinov focusing mask. The mask design is optimised for focal length and aperture of your telescope or lens.

2) Download and run Inkscape (or any other CAD program that can load SVG file and print it. Download form:http://www.inkscape.org

How do you make one?

1) Visit http://astrojargon.net/MaskGen.aspx to obtain a SVG file (scalar vector graphic file) of your Bahtinov focusing mask. The mask design is optimised for focal length and aperture of your telescope or lens.

2) Download and run a piece of freeware called Inkscape (or any other CAD program that can load SVG file and print it. Download form:http://www.inkscape.org

3) Build your mask

An wooden embroidery hoop can be use, with door insulation foam if need be, to attach the mask to and to place over the aperture of the telescope.

Hoops of varying sizes can be bought from a HobbyCraft store or on-line at the following websites:

http://www.hobbycraft.co.uk

http://www.sewandso.co.uk

Expect to pay around £2.00 for one

The End